FIGS. 14 and 15 are a schematic diagram and a block diagram, respectively, of a conventional example of a lighting system. In this conventional lighting system, for the purpose of controlling the lighting of a light fitting 20 (for example, an LED (light emitting diode) light employing a light emitting diode as a light source) installed indoors, an illuminance sensor 50 is used as a means of acquiring information on the indoor illuminance. That is, in this conventional lighting system, by use of the illuminance sensor 50, which is arranged at a spot (or in an area) where constant illuminance is desired, indoor illuminance information is acquired with respect to the illumination light from the light fitting 20 plus the light (sunlight) shining in through a window, and the so acquired illuminance information is fed to the LED driver 30 for the control of the lighting of the light fitting 20.
In addition, in recent years, out of growing ecological concerns, solar power generation has been receiving much attention for the comparatively light burden it inflicts on the earth's environment. Accordingly, the above-mentioned conventional lighting system is so configured that it can use, as the electric power source for the LED driver 30, both commercial electric power and a solar cell 10.
An example of the conventional technology discussed above is seen in Patent Document 1 listed below.